Lightning towers are great. They've always been my favorite of the Apprentice's towers. I use fireball towers to supplement beating back the horde/DPSing ogre spawnzones, and obviously magic missiles are the primary of any apprentice.

As for a staff, yes, you want an actual weapon. I'm a tower-based apprentice, but my actual staff (NM Goblin Overlord staff from Raining Goblins challenge) has been upgraded purely on base damage/additional projectiles. It helps a lot if it has a hero damage buff as well. Tower buffs are nifty too but you should focus upgrading a staff weapon to be an actual weapon, comes in handy when you get a genie too. My staff has gotten so strong I'm even out dps-ing my DPS hunter of the same level which I was surprised by.

Oh, and as Damador said, darkness traps will still be useless because Magic Blockades have always stripped the resistances of anything bashing it.

As for upgrading armor, it's up to you, but on NM as everyone says you'll want to max armor/resistance stats. Good luck.

What stats should I be getting for a tower build Apprentice? Is the chain lightning tower any good? I don't see many people use that tower.

What stats should I be looking for on a weapon? Should I just upgrade weapon damage? What stats should I be upgrading on armor?

Well if you are at the level where you are questioning what towers to use, i doubt you are at the level where u start looking for good weapons. Anyway, you want on with a nice amount of upgrades, projectiles and tower stats. A good starter staff is a nm goblin overcharge staff. You can upgrade all damage and # of projectiles, or level both to a good amount then the rest into tower damage/ rate of fire